Scanners are used to create a scan of pixel values of a document. The scan can be displayed on a computer monitor, can be used by a computer program, can be printed, can be faxed, etc. A first conventional method for scanning a document uses a scanner including a horizontal scan bar having sensor elements (such as CCD [charge-coupled-device] elements). A document on the scanning area of the scanner is scanned by the scan bar. With the scan bar stationary, the scanner obtains pixel values from the sensor elements for corresponding pixel locations of a portion of the document along the horizontal scan line of the scan bar. The scan bar is moved vertically for vertically-displaced successive horizontal scan lines until a scan of the entire document is obtained. In a second conventional method, the scan bar always remains stationary, and the document is scanned by moving the document past the scan bar.
In one known extension of the first and second conventional methods, the pixel values of the scan of the entire document are compensated for background intensity using a calculated gray background pixel level.
Conventional scanning methods include detection of the edges of the document being scanned to exclude from the scan those pixel values obtained from outside the edges of the document. Conventional scanning methods also include segmenting the scan into text pixel areas (such letters and punctuation marks) which are mathematically sharpened, using a sharpening filter, to improve the appearance of the text. Conventional scanning methods further include segmenting the scan into image pixel areas which are mathematically smoothed, using a smoothing filter, to improve the appearance of the image.
What is needed is an improved method for background intensity correction of a scan of pixel values of a document.